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Dinosaur Genus List - ZScipionyx samniticusMonocloniusProtarchaeopteryxMicrovenatorToday's featured page: Migrating Animal Printouts



ZoomDinosaurs.com
Dinosaur and Paleontology Dictionary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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If the dinosaur or paleontology term you are looking for is not in the dictionary, please e-mail us.

Ammonites

(pronounced AM-uh-nites) Ammonites were early mollusks. These marine animals had no vertebrae and were protected by a hard shell (usually coiled) made from calcium. Fast-moving predators, they ate other animals in the sea. They were cephalopods.

Anatomy: These animals were protected by a shell (usually spiral-coiled) that contained many air filled chambers, called phragmocones; the animal lived only in the outer chamber. The opening of the shell is called the aperture. The walls of each chamber are called septa; these walls were penetrated by a ventral tubelike structure called a siphuncle that probably regulated the air pressure, allowing the ammonite to float.

Size: Ammonites ranged in size from under an inch to about 9 feet (3 m) in diameter.

When Ammonites Lived: Ammonites appeared during the Devonian and went extinct during the K-T extinction, 65 million years ago. The closest living relative of the ammonite is the chambered nautilus.

Why Are They Called Ammonites?: Ammonites were named for Amun (also spelled Ammon), an ancient Egyptian god who is pictured as having ram's horns behind each ear (which look like ammonites).

Index Fossils: Ammonite fossils are found in great quantities and are used as an index fossil. Index fossils are commonly found fossils that are limited in time span. They help in dating other fossils.

Ammonites were common during the Mesozoic Era, but are not found after the Cretaceous period (when they went extinct). This knowledge (and knowledge of when particular species of ammonites lived) helps date rarer fossils of unknown age. For example, if a new fossil is found in the same rock layer as an ammonite that is known to have lived only during the Cretaceous period, the new fossil can likely be dated to that same period.



Information Sheets About Dinosaurs
(and Other Prehistoric Creatures)

Just click on an animal's name to go to that information sheet. If the dinosaur you're interested in isn't here, check the Dinosaur Dictionary or the list of Dinosaur Genera. Names with an asterisk (*) were not dinosaurs.
How to write a great dinosaur report.

For dinosaur printouts, click here.

For brief dinosaur fact sheets, click here.




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